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Mr. Russo Beaumont High School Objective: Ch 4.3-4.5 (Pg 40) We will be able to define inertia and explain Newton’s first law of motion. Ch 4.3 – 4.5 Notes Force Force – Any push or pull Friction Friction – Name given to force that acts between materials that touch as they move past each other Inertia Inertia – Every material object resists change in its state of motion (laziness of an object) Figure 4.3 Newton’s st 1 law Newton’s 1st Law (Law of inertia) – Every object continues in a state of rest or of motion in a straight line at constant speed, unless it is compelled to change that state by forces acting upon it. – Newton An object at rest stays at rest, and an object in motion stays in motion without forces acting upon them This reminds me of you Students doing math 2 and 3 step math problems Demos Hanging Mass Penny in a cup Paper and bottle Why do objects slow down and stop? Because of outside forces, mostly because of friction What would happen if you threw an object from a space station? It would go forever Inertia Explained The more mass an object has, the more inertia it has. Less mass, less inertia Is it easier to pick up a toy car or a real car? Inertia is laziness What is mass? Mass – The amount of material present in an object Measure of inertia of an object MASS DOESN’T CHANGE What do we measure mass in? Mass is measured in kilograms What is the difference between mass, volume and weight? Mass Measure of how much matter present (How much inertia) Volume How much space it is taking up. Weight Force of gravity on an object. (Depends on location) To calculate weight we use the formula w = m*g g = force of gravity For Example Mass of boulder = 10 kg Weight of boulder = 0 kg Volume of boulder = 10 L On your white board If a woman has a mass of 50 kg, calculate her weight in Newtons w = mg w = (50kg)(9.8m/s2) w = 490 N On your white board Calculate in newtons the weight of a 2000 kg elephant w = mg w = (2000kg)(9.8m/s2) w = 19,600 N On your white board Calculate in newtons the weight of a 2.5 kg melon. What is the weight in pounds? (4.45 N = 1lb) w = mg w = (2.5kg)(9.8m/s2) w = 24.5 N 24.5 N / 4.45 N = 5.5 lbs On your white board An apple weighs about 1 N. What is its mass in kilograms? What is its weight in pounds? (2.2 lbs = 1 kg) w = mg 1 N = (m)(9.8m/s2) m = 1N / 9.8 m/s2 = .1 kg .1 kg = .22 lbs On your white board Susie finds she weighs 300 N. Calculate her mass. w = mg 300 N = (m)(9.8m/s2) m = 30.6 kg Objective: Ch 4.6-4.9 (Pg 44) Given 2 or more forces we will be able to calculate the net force exerted on an object Notes 4.6 – 4.9, Force Net Force – The combination of all forces acting on an object. Net force changes an objects state of motion What happens if you pull with equal and opposite forces? Nothing! If forces are equal and opposite the net force is zero! What is the minimum # of forces acting on an object at rest? 2 Force of gravity (Down) Normal Force (Up) Normal Force Normal Force – Upward force on an object also called the support force Equilibrium Equilibrium – When all forces on an object cancel out. Net force is zero Object will not move if at rest Draw Figure 4.11 Tension Force Tension Force – When atoms are stretched (As opposed to being compressed) When the angle from vertical increases, what happens to the tension force? Tension always increases as the angle away from vertical increases Slogan: Net Force is zero, of course – Tanner Do you move – Jose Net Force Zero, no excuses – Mia Equilibrium equals net force zero – Michael Are you in motion – Tim Chuck Norris & Mr Russo, Net force ZERO! – JJ Net Force is zero, unless your Chuck Norris Chris What happens if you flip a coin in an airplane while its moving? It behaves as if the plane were at rest. Why? Inertia Objective Ch 5.1-5.4 - What must happen for acceleration to occur? Forces cause acceleration Hockey Puck at rest No Acceleration Player hits puck Acceleration Puck moving across ice No acceleration Acceleration is directly proportional to what? Acceleration is directly proportional to the Net Force acting on it More force = more acceleration Less force = less acceleration Newton’s nd 2 Law Newton’s 2nd Law – The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force and is inversely proportional to the mass of the object. – Newton More Force = More acceleration (Directly Related) More Mass = Less Acceleration (Inversely Related) What is the formula for acceleration? Acceleration = Net force / Mass More commonly F = ma a = F/m m = F/a What are the units for the Newton Force is measured in NEWTONS Force is mass x acceleration Units are kg*(m/s2) Friction Friction – between two objects touching. Always acts in direction opposite to state of motion Fluids Fluids – Gases or liquids ( because they flow) Air Resistance Air Resistance – Friction acting on something moving through air How can acceleration be zero when there is still a force applied? When there is a force applied, the force of friction will balance it out and make net force zero Pressure Pressure - force per unit area P= F/A Terminal Speed / Terminal Velocity Terminal Speed - Object is falling and no longer is accelerating Terminal Velocity – Same thing, direction is down Ch 6.1-6.6 If you push against a wall, how come it doesn’t fall over? Because the wall is pushing back on you. Interaction Interaction – A mutual action between objects where each object exerts equal and opposite forces Newton’s rd 3 Law Newton’s 3rd Law – Whenever one object exerts a force on a 2nd object, the second object exerts an equal and opposite force on the 1st object. In other words – For every action there is an equal and opposite reaction Action / Reaction Force Action /Reaction Forces – Co-parts of a single interaction. One cannot exist without the other. No such thing as a single force Example Action: Earth’s gravity pulls down a boulder Reaction: The boulders gravity pulls up on the Earth Example Action: Rocket pushes gas Reaction: Gas pushes rocket What pushes a car as you drive? Action: Tire pushes against the road Reaction: Road pushes against tire Figure 6.7 H0w come the cannon doesn’t move just as fast backwards as the cannon ball goes forward? A smaller mass has greater acceleration A greater mass has less acceleration Example How come the Earth doesn’t move just as fast up as the boulder goes down? Larger masses have less acceleration Figure 6.8 How does a rocket accelerate? Action Force: Rocket pushes air molecules down Reaction Force: Air molecules pushing rocket up Figure 6.13 – Horse and the Cart How come if forces are equal and opposite, the cart still moves? The friction between the horse and the ground is greater than the cart wheels and the ground F-f